I. Field of the Present Invention
The present invention relates generally to fluid control devices for applying fluid at a predetermined pressure to a working cylinder, and more particularly to means for precisely regulating the pressure of the fluid being applied to the working cylinder.
II. Description of the Prior Art
Working cylinders, such as pneumatic cylinders, are often used to control displacements of robotic arms and the working tools, such as a welder, secured at the end of a robotic arm. For example, such cylinders have been used to extend and retract relatively displaceable welding electrodes to a predetermined welding position on a workpiece. During the actual welding operation, the electrodes are engaged against the workpiece. In previously known welding systems, the quality of the weld is controlled primarily by variations in the weld time as well as the electrical current being applied to the electrodes during the welding period. As a result, previously known displacement cylinders used for controlling the engagement of the electrodes with the workpiece operated repeatedly at a single pressure to merely engage the electrodes against a workpiece.
Unfortunately, reliance upon variations only in the welding current and welding time can result in ineffective welds, damage to the workpiece, undue delay in forming the weld or extremely high energy requirements to form the welds in particular workpieces. For example, the previously known welders are not well adapted for making effective welds in a laminated workpiece formed from layers of different materials. Thus, it has been extremely difficult if not impossible to weld such workpieces in a quick and efficient manner when only variation of the welding current or welding time are available. On the other hand, it has been found that adjustment of the pressure with which the electrodes engage the workpiece can substantially decrease the welding time or current necessary to form the welds in these laminates.
Nevertheless, previously known pressure regulators for adjusting the amount of pressure applied to a working cylinder for an actuating displacement of the electrodes cannot adjust the pressure as accurately and precisely as desired. In particular, previously known pressure regulators may be manually controlled and thus require time as well as labor to operate. Moreover, manual control of the valves can result in inaccurate adjustment of the valves and the actual pressure delivered at a nominal setting can vary throughout a wide range. In view of the fact that variations in the pressure at which the electrodes are engaged against the workpiece can substantially affect the effectiveness and the efficiency of a welding operation as well as the quality of the welds and the finished workpiece, more accurate and precise control of the pressure applied to the working cylinder can enhance the productivity of the entire assembly process in which the welding operation occurs.